1. Technical Field
The present invention relates to a capacitor and its manufacturing method, and a semiconductor device equipped with the capacitor.
2. Related Art
Various kinds of capacitors are used in semiconductor devices as their constituting elements (see, for example, Japanese Laid-open Patent Application HEI 7-226485, Japanese Laid-open Patent Application HEI 9-139480, Japanese Laid-open Patent Application HEI 5-82801, and Japanese Laid-open Patent Application HEI 5-47587Patent). For example, capacitors are used in oscillation circuits, power supply circuits and the like in semiconductor devices for the purpose of prevention, stabilization and smoothing of oscillations of operation amplifiers, for voltage step-up circuits, and the like.
Such capacitors often use a structure, in the case where they are fabricated inside circuits, in which an insulation film (dielectric film), such as, a silicon oxide film, silicon nitride film, silicon oxinitride film or the like is sandwiched between upper and lower electrode films composed of silicon or metal, or titanium nitride, aluminum nitride or the like. Also, in the case where they are attached externally to circuits or the like, capacitors such as laminated capacitors equipped with ceramics insulation films (dielectric films), such as, barium titanate films or the like are known.
When such capacitors are fabricated, in particular, when their insulation films are formed, a sputter method, a CVD method, a laser ablation method or the like is normally employed.
It is noted that the capacity of a capacitor is in proportion to the dielectric constant and area of an insulation film (dielectric film) thereof, and in reverse proportion to the thickness of the insulation film. Accordingly, when capacitors of a small size and high capacity are desired to be formed inside circuits, their insulation films (dielectric films) may preferably be formed from a material having a high dielectric constant in view of leak current, to thereby achieve a high capacity. On the other hand, when capacitors are externally mounted, it is desirous if they can be readily fabricated with thin films as there are demands to lower assembly costs, and improve the yield.
Under such circumferences, the dielectric constant of an insulation film (dielectric film) of a capacitor may preferably be 300 or greater in the case of internal circuits, and 1000 or greater in the case of externally attached type, in consideration of its area and film thickness.
However, the capacitor fabricated inside the circuit described above uses a silicon oxide film, a silicon nitride film, or a silicon oxinitride film as an insulation film, and these insulation films (dielectric films) have low dielectric constants, which are 10 or less. Accordingly, it may be necessary to increase its area to increase its capacity. However, when the area of the capacitor is increased, an area occupied by the capacitor in the circuit becomes larger, which prevents miniaturization of the circuit.
As insulation materials having a high dielectric constant, ferroelectric materials, such as, for example, lead zirconate titanate (PZT), barium titanate and the like are known. Film forming temperature for those ferroelectric materials needs to be 450° C. or less in view of its influence to other semiconductor elements and wirings provided in the same semiconductor device. However, because crystallization is difficult to take place at such a low temperature, the resultant ferroelectric film obtained may not attain a desired level of high dielectric constant, although it may have a relatively high dielectric constant compared to silicon oxide films. Also, the dielectric constant changes greatly against changes in frequency and temperature, and therefore the ferroelectric film may be inferior compared to silicon oxide films.
Also, in the method for manufacturing such capacitors, in particular, because their insulation films are formed by a sputter method, a CVD method, a laser ablation method or the like, there are problems in that a large scale film forming apparatus is necessary, which requires a high initial cost, and a large amount of energy is necessary for film formation, which requires a high running cost. Also, when patterning is conducted by etching after film formation, there are problems in that the material usage efficiency is poor, and photolithography masks and chemicals for etchings are necessary, which result in a higher cost, and the number of steps increases, which lowers the productivity.
On the other hand, when capacitors composed of ceramics such as barium titanate or the like that are externally mounted are formed, although the cost of the capacitors themselves may be lowered, the assembly cost is required for positioning at the time of external mounting, bonding with other elements and the like, and there are problems in the yield, such that a sufficient cost reduction has not been achieved.
Also, piezoelectric elements having insulation films of PZT or the like that include Pb in their compositions may possibly become a source of environmental pollution as Pb is a toxic substance, such that reconsideration of the production of piezoelectric elements using this material would be driven in future by necessity.
The present invention has been made in view of the problems described above, and its object is to provide a capacitor that has an insulation layer of a high dielectric constant and does not contain Pb, which can therefore make it possible to reduce the size of a device having the same, and which is environmentally advantageous, a method for manufacturing a capacitor which makes it possible to manufacture the capacitor at a low cost, and a semiconductor device equipped with the capacitor.